System and method for spinal fusion

ABSTRACT

The current invention is directed to a system and method for fusing two adjacent vertebrae. In one embodiment, the vertebrae are fused by inserting a self-broaching interbody apparatus into a disc space without the need for separately drilling and broaching. The self-broaching interbody apparatus may include cutting flutes or other broaching means capable of cutting through the cartilaginous endplates of the vertebrae. In another embodiment, an interbody apparatus with an expanding means capable of distracting the disc space between the adjacent vertebrae is inserted into the disc space. Another embodiment includes a sleeve that fits around an interbody apparatus that has at least one opening in its outer surface leading to a cavity filled with bone and/or ortho-biological materials.

BACKGROUND

As the lumbar spine ages, disc degeneration occurs. This degenerationcauses a reduction in the vertical height of the disc, and a diminutionof its viscoelastic properties. The profile of the spine also changeswith age. The swayback curvature of youth becomes the flat-back of oldage. This results in increased biomechanical stress on the posteriorside of the spine.

With a recent increased understanding in the biomechanics of the spine,it is acknowledged that maintenance of the normal curvature of thelumbar spine is preferable. When spinal fusions are considered, it isimportant to re-establish the normal biomechanical arrangement, and torestore the sagittal profile of the spine to obtain optimal results.Arthritic changes in the facet joints following disc degeneration cancause mechanical back pain. If they become excessive, these arthriticchanges can cause spinal stenosis.

For these reasons, several prior art techniques have been used thatremove the degenerated disc, distract the disc space, and rigidly bondthe upper and lower adjacent vertebrae together. Initially, this wasaccomplished by inserting pieces of bone having cortex and marrow cutfrom solid bone locations, such as the wing of the pelvis or the fibula.Such grafts were only able to support around 430 lbs. of force withinthe disc space, however, and compression forces up to 1,850 lbs. can beexperienced by a human when, for example, bending over to pick up a 25lb. child. After experiencing such high compression forces, these graftstended to collapse and lose their ability to fix and stabilize thespinal motion segment by distracting the disc space.

To deal with this problem, metal cages packed with bone orortho-biological compounds (osteoinductive/osteoconductive) capable offusing with the adjacent vertebrae were inserted in the distracted discspace. Such cages were able to withstand the larger compression forceswhile allowing the bone inside of the cages to fuse with the adjacentvertebrae. The cages were typically constructed of titanium meshcylinders, screw-in bullet-like metal cages with external threads, orrectangular cages made of carbon fiber.

These cages were typically inserted into the disc space after the spacehad been distracted and/or drilled by a separate tool to form a nichefor the cage and to broach through the cartilage and into the boneytissue to promote fusion. For purposes of this disclosure “broaching”refers to cutting through the cartilage of adjacent vertebral endplatesand into the boney tissue of the vertebrae. The process of separatelybroaching and distracting the disc space, however, requires multiplesteps of inserting and removing various drills, broaches and/ordistracters into the disc space, causing direct or indirect damage tothe load-bearing endplates of the adjacent vertebrae, weakening them andjeopardizing the fixation of the interbody fusion construction.

Because of the openings in the cages, another problem with the prior artcages were that small pieces of bone or ortho-biological material werecapable of spilling out of the cage and into the soft tissue surroundingthe surgical opening before the cage was placed between the vertebralendplates. In this case, heterotrophic ossification, or bone growth,could occur in the access port of the surgical wound or possibly nearthe exiting segmental nerve, resulting in bony nerve entrapment andtremendous pain and complications.

Other prior art methods of distracting the disc space included insertinga semi-rigid, U-shaped object with internal teeth. A round object with alarger diameter than the interior space of the object was then insertedinto the interior space between facing interior teeth. By moving theround object further into the interior of the object, the legs of theU-shaped object were pushed apart, thereby distracting the disc space.These U-shaped devices, however, typically broke due to the forcesexerted by the round object and the adjacent vertebrae.

In addition to the above problems with inserting the prior art cages,the cages are susceptible to movement within the disc space once theyare inserted. This movement can damage the biological growth of thefusion, due to shear forces on the vascular ingrowth nourishing theendosteal bone growth—limiting the development of fusion of the boneinside of the cage which is necessary to stabilize the adjacentvertebrae, resulting in looseness and bone graft collapse. To thiseffect, several prior art cages were constructed with short spikes orpoints to stabilize them within the disc space, but which were not longenough to broach through the cartilage into the boney tissue of thevertebrae.

Moreover, if the compression forces are not withstood and the disc spaceis not held in a distracted state by a strong cage, the cage maycollapse, leading to looseness, instability and further failure offusion due to movement. However, if the cage is overly rigid and strong,such as a threaded cage, it may shield the bone inside of the cage fromthe normal stresses and strains that bone needs to develop into weightbearing, trabecular bone, which will fuse with the adjacent vertebrae ina strong and rigid fashion. This failure to satisfactorily promotefusion may also lead to looseness and instability of the cage or fusionconstruct.

Therefore, a need exists to provide an interbody device or a method ofinserting such a device that solves one or more of the problemsdescribed above.

SUMMARY OF THE INVENTION

The current invention is directed to a system and method for fusing afirst and second vertebrae. In one embodiment, the vertebrae are fusedby inserting a self-broaching interbody device into a disc space withoutthe need for separately drilling and broaching. The self-broachinginterbody device may include cutting flutes or other broaching meanscapable of cutting through the cartilaginous endplates of thevertebrae˜exposing subchondial bone, facilitating fusion development.

In another embodiment, an interbody device with an expanding means isinserted into the disc space. The expanding means is capable of movingthe interbody device from an unexpanded state, where the upper and lowersurfaces of the interbody device are at a first distance from eachother, to an expanded state, where the upper and lower surfaces are at asecond and greater distance from each other. In the unexpanded state,the interbody device can be inserted between the vertebrae while theyare in an undistracted state without the need for previously distractingthe disc space. In the expanded state, the inserted interbody device canforce the first and second vertebrae into a distracted state.

Yet another embodiment includes a sleeve that fits around an interbodydevice that has at least one opening in its outer surface leading to acavity. Bone graft and/or ortho-biological materials capable of fusingwith the vertebrae are contained within the sleeve's cavity. The sleeveis configured to fit around the interbody device so that the biologicalmaterials are kept within the cavity while the interbody device iswithin the sleeve. The interbody device can then by moved completelythrough the sleeve to rest between the vertebrae.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings where:

FIG. 1 is a top view of one embodiment of an interbody system accordingto the invention;

FIG. 2 is a side view of the embodiment shown in FIG. 1, inserted intoadjacent vertebrae;

FIG. 3 is a front view of the nose of the embodiment shown in FIGS. 1and 2;

FIG. 4 a is a side cross-sectional view of another embodiment of aninterbody system according to the invention;

FIG. 4 b is a front perspective view of an end of the insertion rodshown in FIG. 4 a;

FIG. 4 c is a top view of the embodiment shown in FIG. 4 a;

FIG. 4 d is an alternate embodiment of the middle septum shown in FIG. 4a;

FIG. 5 is a side cross-sectional view of another embodiment of aninterbody cage system according to the invention;

FIG. 6 is a side perspective view of yet another embodiment of aninterbody cage system according to the invention;

FIG. 7 a is a side perspective view of still yet another embodiment ofan interbody cage system according to the invention in an unexpandedstate;

FIG. 7 b is a side perspective view of the embodiment shown in FIG. 7 ain an expanded state; and

FIG. 8 is a side perspective view of an alternate embodiment of theinvention inserted into a surgical opening toward the spine.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a top view of an interbody cage 1 and an insertion rod 10.The cage 1 includes a substantially square and hollow main portion 2 anda nose 26. Bone graft with biological materials, such as morphogenicprotein and derivatives, can be placed inside of the cage 1 to allow thecage 1 to be fused and incorporated into the boney structure of theadjacent vertebrae once the cage 1 is inserted.

The insertion rod 10 projects through axial openings 12 and 14 of theback wall 16 and middle septum 18, respectively, of the cage 1. A distalend 20 of the insertion rod 10 abuts an internal, distal end 22 of thecage 1, and is shaped to match the internal, distal end 22 of the cage1. This shape serves to evenly distribute an insertion force exerted bythe insertion rod 10 onto the internal, distal end 22 of the cage 1.

The middle septum 18 of the cage L comprises a rigid girder fixed to theinterior surface of the cage 1 and located in a plane transverse to theprojection of the insertion rod 10. The middle septum 18 serves tostabilize the insertion rod 10 and to increase the center strength ofthe generally hollow cage 1. The middle septum 18 may also includeinternal threads that mate with external threads on the insertion rod10. Mating of these threads can more evenly distribute the force exertedon the insertion rod to the cage 1. In other embodiments of the cage,the middle septum 18 is not included or is replaced by several girdersdisposed on either side of the insertion rod.

The back wall 16 can be double welded to the back edge of the cage 1 toallow for increased vertical and horizontal strength of the cage 1. Theopening 12 in the back wall 16 may alternatively include internalthreads that can mate with external threads on the inserting rod 10. Inthis embodiment, the mating of the threads can aid in the insertionforce transmitted from the inserting rod 10 to the cage 1.

In this embodiment, the cage 1 has a generally parabolic nose 26. Theparabolic shape can aid in the distraction of the disc space between theadjacent vertebrae (shown in FIG. 2) by slowly separating themvertically as the nose 26 is inserted into the disc space.

As shown in the side view of FIG. 2, the cage 1 has fenestrations 28, oropenings, along its sides. These fenestrations allow bone graft withinthe main portion 2 to fuse with adjacent vertebrae outside of the cage1.

Cutting flutes 24 are disposed in two lines along each upper and lowersides of the nose 26. The cutting flutes 24 project from the nose 26 ina generally vertical direction, in a manner similar to a Sampson nail.The cutting flutes 24 are long enough to broach through the cartilage ofthe vertebral endplates and into the boney tissue. For purposes of thisdisclosure, “self-broaching” refers to the interbody device's ability tobroach through the cartilaginous endplates of a vertebra on its own,exposing subchondral bone. In one embodiment, the flutes 24 are between1-3 mm long. By broaching into the vertebrae, the cage 1 can allow theblood and tissue from the adjacent vertebrae to mix with the bone graftwithin the cage 1 to promote fusion.

As the cage 1 is inserted postero-laterally in the disc space betweenupper and lower adjacent vertebrae 30 and 32, the nose 26 slowlydistracts the disc space between the vertebrae 30 and 32 as theinsertion rod 10 is pushed in the insertion direction. The distractingcage 1 also protects the load-bearing endplates 38 of the adjacentvertebrae 30 and 32 from damage resulting from prior art distraction anddrilling methods.

As the cage 1 slides along the adjacent vertebrae, the cutting flutes 24cut tracks 34 into the adjacent vertebrae 30 and 32. In this embodiment,keel edges 35 are disposed along in two lines along each of the upperand lower sides of the main portion 2, which trail behind the cuttingflutes 24 within the tracks 34 to maintain the alignment of the cage 1with the adjacent vertebrae 30 and 32. In addition to cutting tracks 34for alignment purposes, cutting flutes 24 broach into the vertebrae 30and 32, releasing blood and tissue, which aid in the fusion of the bonegraft located within the cage 1.

A front view of the nose 26 is shown in FIG. 3. The top, bottom and sidesurfaces of the nose 26 are concave, with the cutting flutes 24extending vertically outward from the center of the nose 26. Thisconcavity allows the cutting flutes 24 to slide into the disc space withminimal friction, reducing the chances of hang up.

The substantially parabolic, fluted nose 26 allows the cage 1 to beself-broaching and self-aligning as it is pushed into the disc space bythe insertion rod 10. This allows the preliminary steps of separatelydistracting the disc space and/or drilling an opening in the disc spaceto be eliminated. A second cage can then be inserted postero-laterallyinto the disc space, and additional bone graft inserted between thecages.

The nose can also include a central opening (not shown) to allow foranterior extraction or correction of the cage 1. In this embodiment, athreaded insertion rod 10 is inserted through this opening and threadedinto threaded openings 14 and 12 in the middle septum 18 and back wall16, respectively. The insertion rod 10 can then be pulled anteriorly topull the cage 1 out from the disc space or to push the cage 1 intobetter alignment within the disc space.

In this embodiment, the cutting flutes 24 of the self-broaching cage 1can cut tracks in the adjacent vertebrae to guide the cage 1 into placeand expose bleeding subchondral bone to facilitate vascular ingrowth andpromote fusion. In addition, the cutting flutes 24 can lock the cage 1in place after the disc space is distracted.

A sleeve 800, shown in FIG. 8, may be fitted around the cage 1 to coverthe fenestrations 28 and open areas of the cage 1 and to keep the bonegraft from exiting the cage 1 before the cage 1 is seated between thevertebrae 30 and 32. The sleeve 800 is substantially the same length asthe insertion rod 110. The sleeve 800 surrounds the cage 1 and isinserted into a surgical opening 870, directed toward the vertebrae 30and 32, avoiding the exiting nerve root 872. As the cage 1 is insertedinto the disc space by passing through the sleeve 800, the sleeve 800 isslowly retracted or kept in place by abutting the adjacent vertebrae,allowing the bone graft to be released in the disc space.

Although the embodiment shown in FIG. 8 shows a sleeve 800 with asubstantially rectangular cross-section, it is within the scope of theinvention to form the sleeve with any shaped cross section. Preferably,the outer surface of the sleeve is shaped to provide easy insertion intothe surgical opening or speculum (not shown), if one is present. Theinner surface cross-sectional dimensions of the sleeve are preferablysubstantially the same as the outer surface dimensions of the cage, forexample, extending approximately 0.5 mm to 3 mm to either side of theprosthesis, and more preferably about 1 mm to ether side.

The sleeve can be made of rigid plastic or any other suitable material,such as flexible plastic, metal, or bio-absorbable implant materials. Inthis embodiment, the sleeve 800 can not only prevent the bone graft fromescaping from the cage 1 before insertion into the disc space, but canalso protect the soft tissues and nerves surrounding the insertion pathfrom damage. Preventing pieces of bone and ortho-biological materialfrom falling into the approach wound can be important as bone canotherwise grow spontaneously if lost in the soft tissue, particularly ifit grew around an exiting segmental nerve. Thus, the embodiment of thesnugly-fitting sleeve 800 can contain and seal the prosthesis until ithas docked in the disc space, substantially avoiding the possibility ofheterotropic ossification.

In the embodiment shown in FIGS. 4 a-4 c, the cage 100 is alsoprogressively self-distracting. Similar to the embodiment shown in FIGS.1-3, the cage 100 includes cutting flutes 124 and fenestrated side wallswith upwardly projecting keel edges 135. The cage 100 also includesupper and lower surfaces 134 and 136 that are vertically movablerelative to each other. The upper and lower surfaces 134 and 136 includetwo sets of internal threads 140 and 142, each set having a spaceseparating them that increases toward the nose 126. A middle septum 118has external threads 144 that mate with the internal threads 140 of theupper and lower surfaces 134 and 136. A back wall 116 also has externalthreads 146 that mate with the internal threads 142 of the upper andlower surfaces 134 and 136.

Both the middle septum 118 and the back wall 116 have hexagonal centralopenings 114 and 112. An insertion rod 110 has a hexagonal cross sectionalong its axis that, when inserted through the central openings 112 and114 and rotated, rotates the middle septum 118 and the back wall 116within the threads 142 and 144. As the middle septum 118 and back wall116 are threaded closer to the nose 126, upper and lower surfaces 134and 136 are pushed farther away from each other. As the surfaces 134 and136 are pushed apart vertically, they distract the disc space further,correcting the alignment of the spine and locking the cage 100 in placebetween the adjacent vertebrae. This distraction is preferably gradualand progressive, produced by the application of measured and calibratedtorque. This allows the surgeon to tailor the distraction to theindividual patient and to predict with relative certainty thedistraction produced by a given amount of torque. Progressivedistraction additionally tightens the anatomy and ensures stability.

Anterior opening 150 in the nose 126 allows an insertion rod 110 to beinserted from the anterior side of the spine into the cage 100. If asurgeon desires to change the distraction of the disc space or to removeor change the position of the cage 100, the insertion rod 110 can againbe inserted through openings 114 and 112, and rotated to thread the backwall 116 and middle septum 118 away from the nose 126, thus collapsingthe space between surfaces 134 and 136.

In FIG. 4 d, an oblong cam 318 is shown that can be used in place of thethreaded middle septum 118 and internal threads 140. Oblong cam 318 canbe rotated within an internal groove (not shown) in a cage to have itslonger diameter aligned vertically. Small slits can be made in the upperand lower surfaces through which the tips of the oblong cam 318 wouldextend when it is vertically aligned. Because of the force from theadjacent vertebrae when the cage is in an expanded state, the slits inthe upper and lower surfaces would lock the oblong cam in verticalalignment once the tips of the oblong cam 318 pass the slits. A similaroblong cam can be used to replace the back wall 116 and internal threads142 in the embodiment shown in FIG. 4 a.

FIG. 5 shows another embodiment of a self-broaching and self-distractingcage 200. Cutting flutes 224 are aligned along nose 226 in a mannersimilar to the embodiment shown in FIGS. 1-3 to allow the cage 200 to beself-broaching. Cage 200 also includes a threaded middle septum 218within internal threads 240 that converge toward the nose 226, similarto the middle septum 118 shown in FIG. 4 a.

In this embodiment, the back walls 216 and 217 are formed as overlappingrectangles that each have a groove-type opening 212, allowing theinsertion rod 210 to project through the overlapping area. Theoverlapping portions of back walls 216 and 217 have interlocking teeth246. The interlocking teeth 246 of each of the back walls 216 and 217project toward the other of the back walls 217 and 216 so that, when theupper and lower surfaces 234 and 236 move away from each other, theyratchet up the vertical height of the posterior side of the cage 200until the corners of the back walls 217 and 216 indent into the adjacentvertebrae to stop the cage from extruding from the disc space.

By locking the vertical height of the posterior side of the cage 200,the force on the cage 200 from the distraction of the disc space isdistributed along the main portion 202 of the cage 200, making collapseof the cage 200 due to those forces less likely.

If a surgeon wishes to remove the cage 200, the insertion rod 210 can beinserted through anterior opening 250, and openings 214 and 212 torotate the middle septum 218 so that it is threaded away from the nose226, collapsing the center portion of the cage 200. The insertion rod ora screwdriver-type tool can be used that would allow a surgeon todisconnect the interlocking teeth 246 by tapping or flicking the backwalls to disengage the teeth. When the teeth are disengaged, the forceon the back walls would then bend them into a V-shape after the centerportion of the cage 200 is collapsed.

In each of the embodiments discussed above, the fenestrated walls of thecage can be cut or stamped out from metal or absorbable biologicalmaterial mesh prior to cage formation. Preferably, the metal would betitanium, stainless steel, alloys or carbon fiber. Alloys such as poroustitanium-nickel alloy have been shown to promote rapid tissue ingrowth.

The cutting flutes or keel pieces can be formed by cutting thefenestrated metal in a line that passes through several of thefenestrations. This results in an edge with several sharp protrusions.This edge can then be electrostatically welded to another similar edgefor increased strength.

Although one skilled in the art will understand that the dimensions ofthe cages and insertion rods can be varied for the desired result, ithas been found that a length of between 22 mm and 30 mm, a height ofbetween 8 mm and 19 mm, and a transverse diameter of 8 mm to 12 mm isideal. The cages are preferably of graduated sizes to accommodate thevariation of human anatomical size. The vertical height in thedistracting embodiments may increase an additional 1.5 mm in eachdirection.

FIG. 6 shows another embodiment of a self-distracting cage 400. In thisembodiment, the cage 400 is formed from two wedge-shaped, hollowportions 434 and 436. A screw 460 projects through internal threads inthe anterior and posterior openings 450 and 412 and has a screw head 462and 464 at both ends so that the screw 460 cannot disengage with thethreads of either opening 450 or 412.

The screw heads 462 and 464 can mate a screw driver (not shown) to berotated while inside of the disc space. As the screw 460 is rotatedwithin the threads of openings 450 and 412, the wedge-shaped portions434 and 436 slide over each other and distract the disc space. The screwheads 462 and 464 can be rotated either posteriorly or anteriorly todistract or collapse the disc space.

FIGS. 7 a and 7 b show an alternate embodiment of the slip-wedge cageshown in FIG. 6. In this embodiment, the cage 500 has domed andself-broaching wedge-shaped portions 534 and 536. Cutting flutes 524project vertically in two lines along each of the top and bottomwedge-shaped portions 534 and 536, similar to the cutting flutes of theprevious embodiments.

As the cage 500 is being inserted between adjacent vertebrae, thewedge-shaped portions 534 and 536 have only a minimal overlap, to ensurethat the cage can be inserted into the disc space with itsself-broaching cutting flutes 524 with minimal resistance. Once the cageis between the adjacent vertebrae 30 and 32, the screw 560 can berotated by a screw driver (not shown) to pull the wedge-shaped portionstoward each other, to distract the disc space. The dome shaped portions534 and 536 allow the force of distraction to be evenly distributedacross the cage, making unintentional collapse less likely.

In each of the embodiments discussed above, reflective fiducials can beadded to the cage and the insertion rod to allow them to be used inimage guided surgery.

Although specific embodiments are disclosed herein, it is expected thatpersons skilled in the art can and will design alternate embodiments andmethods that are within the scope of the following claims eitherliterally or under the doctrine of equivalents.

1. An spinal fusion system for fusing two adjacent vertebrae, comprisinga self-broaching interbody apparatus with an inside surface, an outsidesurface, an insertion end and a trailing end, the interbody apparatusconfigured to be inserted between said adjacent vertebrae.
 2. The spinalfusion system of claim 1, wherein the insertion end includes cuttingflutes, the cutting flutes projecting from the outside surface in afirst direction and configured to cut through a cartilage layer on atleast one of said adjacent vertebrae.
 3. The spinal fusion system ofclaim 2, further comprising a keel projecting in substantially the firstdirection, fixed to the outside surface and aligned behind at least oneof the cutting flutes.
 4. The spinal fusion system of claim 1, whereinthe trailing end includes an edge that projects at least partiallyoutward, such that when the interbody apparatus sits between saidadjacent vertebrae, the edge exerts force on said adjacent vertebrae. 5.The spinal fusion system of claim 1, wherein the interbody apparatusfurther comprises an upper surface, a lower surface and an expandingmeans, wherein the expanding means is capable of moving the interbodyapparatus from an unexpanded state, where the upper and lower surfacesare at a first distance from each other, to an expanded state, where theupper and lower surfaces are at a second and greater distance from eachother.
 6. An spinal fusion system for fusing a first and second adjacentvertebrae, comprising a sleeve with an insertion end, a trailing end, aninside surface and an outside surface, the inside surface sized tocontain an interbody apparatus, the outside surface sized to beinsertable into a surgical opening, and the insertion end and thetrailing end having openings.
 7. The spinal fusion system of claim 6,wherein a distance between the inside surface of the sleeve and an outersurface of the interbody apparatus is approximately 0.5 mm to 3 mm. 8.The spinal fusion system of claim 6, wherein a distance between theinside surface of the sleeve and an outer surface of the interbodyapparatus is approximately 1 mm.
 9. The spinal fusion system of claim 6,further comprising an interbody apparatus with an outside surface, theinterbody apparatus configured to fit within the inside surface of thesleeve and able to slide through the insertion end opening of thesleeve.
 10. The spinal fusion system of claim 9, further comprising asubstantially rigid insertion rod sized to fit through the trailing endopening of the sleeve.
 11. The spinal fusion system of claim 10, whereinthe sleeve is approximately the same length as the insertion rod. 12.The spinal fusion system of claim 9, wherein the outer surface of theinterbody apparatus comprises an opening into a body cavity thatcontains at least one of bone and ortho-biological materials capable offusing with said adjacent vertebrae, and wherein the inner surface ofthe sleeve fits around the outer surface of the interbody apparatus suchthat the openings are enclosed by the sleeve and the at least one ofbone and ortho-biological materials are kept substantially within thecavity.
 13. The spinal fusion system of claim 9, wherein the interbodyapparatus is self-broaching.
 14. The spinal fusion system of claim 6,wherein the sleeve comprises plastic.
 15. The spinal fusion system ofclaim 6, wherein the sleeve comprises metal.
 16. The spinal fusionsystem of claim 6, wherein the sleeve comprises bio-absorbable material.17. The spinal fusion system of claim 6, wherein the sleeve is rigid.18. The spinal fusion system of claim 17, wherein the outer surface ofthe sleeve at the insertion end is larger than a distance between saidadjacent vertebrae.
 19. The spinal fusion system of claim 6, wherein thesleeve is flexible.
 20. An spinal fusion system for fusing two adjacentvertebrae, comprising: an interbody apparatus with an upper surface, alower surface, an insertion end and a trailing end; and an expandingmeans capable of moving the interbody apparatus from an unexpandedstate, where the upper and lower surfaces are at a first distance fromeach other, to an expanded state, where the upper and lower surfaces areat a second and greater distance from each other, wherein in theunexpanded state, the interbody apparatus can be inserted between saidadjacent vertebrae while a distance between the adjacent vertebrae is inan undistracted state, and wherein in the expanded state, the interbodyapparatus can force the distance between the adjacent vertebrae into adistracted state.
 21. The spinal fusion system of claim 20, wherein theexpanding means comprises: upper internal threads fixed to the uppersurface and projecting toward the lower surface, the length of the upperinternal threads increasing toward the insertion end; lower internalthreads fixed to the lower surface and projecting toward the uppersurface, the length of the lower internal threads increasing toward theinsertion end; and a disc having external threads mated with the upperand lower internal threads, such that when the disc is threaded towardthe insertion end, the upper and lower surfaces are pushed apart. 22.The spinal fusion system of claim 21, wherein the expanding meansfurther comprises: rear upper internal threads fixed to the uppersurface near the trailing end and projecting toward the lower surface,the length of the rear upper internal threads increasing toward theinsertion end; rear lower internal threads fixed to the lower surfacenear the trailing end and projecting toward the upper surface, thelength of the rear lower internal threads increasing toward theinsertion end; and a back wall disc having external threads mated withthe rear upper and rear lower internal threads, such that when the backwall disc is threaded toward the insertion end, the rear upper and rearlower surfaces are pushed apart.
 23. The spinal fusion system of claim21, wherein the expanding means further comprises: an upper back wallfixed to the upper surface near the trailing end, the upper back wallprojecting toward the lower surface and including upper ratchets; and alower back wall fixed to the lower surface near the trailing end, thelower back wall projecting toward the upper surface and including lowerratchets, the lower back wall overlapping with the upper back wall in anarea of overlap, wherein the upper ratchets and lower ratchets projecttoward each other and interlock, such that when the upper and lowersurfaces are moved toward the expanded state, the upper ratchets andlower ratchets interlock with a decreasing area of overlap.
 24. Thespinal fusion system of claim 21, wherein the disc has an opening, theexpanding means further comprising an insertion rod configured to fitwithin the opening such that when it is rotated, the disc rotates withit.
 25. The spinal fusion system of claim 20, wherein the expandingmeans further comprises: a first oblong cam having a first major radius,the first cam in a substantially perpendicular plane to the upper andlower surfaces inside of the interbody apparatus and rotatable withinfirst grooves in the upper and lower surfaces, wherein the first cam isshaped such that when it is rotated, the interbody apparatus movesbetween an expanded state, where the first major radius points towardthe upper and lower surfaces and pushes them away from each other, to anunexpanded state, where the first major radius points away from theupper and lower surfaces.
 26. The spinal fusion system of claim 25,wherein the expanding means further comprises: a second oblong camhaving a second major radius, the second cam in a substantiallyperpendicular plane to the upper and lower surfaces inside of theinterbody apparatus and rotatable within grooves near the trailing endin the upper and lower surfaces, wherein the second cam is shaped suchthat when it is rotated, the interbody apparatus moves between anexpanded state, where the second major radius points toward the upperand lower surfaces and pushes them away from each other, to anunexpanded state, where the second major radius points away from theupper and lower surfaces.
 27. The spinal fusion system of claim 25,wherein the expanding means further comprises: an upper back wall fixedto the upper surface near the trailing end, the upper back wallprojecting toward the lower surface and including upper ratchets; and alower back wall fixed to the lower surface near the trailing end, thelower back wall projecting toward the upper surface and including lowerratchets, the lower back wall overlapping with the upper back wall in anarea of overlap, wherein the upper ratchets and lower ratchets projecttoward each other and interlock, such that when the upper and lowersurfaces are moved toward the expanded state, the upper ratchets andlower ratchets interlock with a decreasing area of overlap.
 28. Thespinal fusion system of claim 25, wherein the upper surface includes anupper slit and the lower surface includes a lower slit, the upper andlower slits located such that the first oblong cam projects at leastpartially through the upper and lower slits when the interbody apparatusis in the expanded state.
 29. The spinal fusion system of claim 25,wherein the first cam has an opening, the expanding means furthercomprising an insertion rod configured to fit within the opening suchthat when it is rotated, the first cam rotates with it.
 30. The spinalfusion system of claim 20, wherein the expanding means furthercomprises: a first end wall projecting from the upper surface on one ofthe insertion end and the trailing end toward the lower surface andhaving a first opening with internal threads; a second end wallprojecting from the lower surface on the other of the insertion end andthe trailing end toward the upper surface and having a second openingwith internal threads; first and second sidewalls having first andsecond projecting edges, the first and second sidewalls fixed to theupper surface and the first end wall, and increasing in size toward thefirst end wall; third and fourth sidewalls having third and fourthprojecting edges, the third and forth sidewalls fixed to the lowersurface and the second end wall, and increasing in size toward thesecond sidewall; a second end wall projecting from the lower surface onthe other of the insertion end and the trailing end toward the uppersurface, the second end wall coupled to the third and fourth sidewallsand having an opening with internal threads; and a linking screw withexternal threads that mate with the internal threads of the first andsecond end walls such that the first and second end walls are pulledtoward each other when the linking screw is rotated, wherein the firstand third projecting edges slide against each other and the second andfourth projecting edges slide against each other when the linking screwis rotated.
 31. The spinal fusion system of claim 30, wherein the upperand lower surfaces are curved to mate with said adjacent vertebrae. 32.A method for fusing two adjacent vertebrae having respectively first andsecond facing cartilaginous endplates, the method comprising: providinga self-broaching interbody apparatus configured to be inserted betweensaid adjacent vertebrae; and inserting the interbody apparatus betweenthe adjacent vertebrae, such that the interbody apparatus broachesthrough at least one of said first and second cartilaginous endplates asit is being inserted.
 33. A method for fusing two adjacent vertebraehaving an undistracted state and a distracted state, comprising:providing an interbody apparatus having an unexpanded state and anexpanded state; inserting the interbody apparatus in the unexpandedstate between said adjacent vertebrae while said adjacent vertebrae arein an undistracted state; and moving the interbody apparatus to theexpanded state after inserting to move the adjacent vertebrae to adistracted state.
 34. A method for fusing two adjacent vertebrae,comprising: providing an interbody apparatus having at least one cavitytherein that opens to an outer surface of the interbody apparatus, thecavity containing at least one of bone and ortho-biological materialcapable of producing a fusion between said adjacent vertebrae; providinga sleeve configured to at least partially surround the interbodyapparatus and hold the at least one of bone and ortho-biologicalmaterial within the cavity; positioning the sleeve at an opening betweensaid adjacent vertebrae; and moving the interbody apparatus completelythrough the sleeve and between said adjacent vertebrae.